JP4784922B2 - Group III nitride crystal production method - Google Patents

Description

The present invention relates to a group III nitride crystal production method for a group III nitride crystal grown in a reaction system using an alkali metal and nitrogen.

  Currently, InGaAlN-based (Group III nitride) devices used as purple-blue-green light sources are mainly used for MO-CVD (metal organic chemical vapor deposition) and MBE (on sapphire or SiC substrates). It is manufactured by a crystal growth method using a molecular beam crystal growth method) or the like. When sapphire or SiC is used as a substrate, there are problems such as an increase in crystal defects due to a large difference in thermal expansion coefficient and lattice constant from Group III nitride.

For this reason, it has the fault that device characteristics are bad, for example, it is difficult to lengthen the lifetime of a light emitting device, or operating power becomes large.
Furthermore, when a sapphire substrate is used as the substrate, since this substrate is insulative, it is impossible to take out an electrode from the substrate side as in a conventional light emitting device, and the surface of the nitride semiconductor surface on which the crystal has grown is impossible. It is necessary to take out the electrode from. As a result, there is a problem that the device area becomes large, leading to high costs.

  Further, the group III nitride semiconductor device fabricated on the sapphire substrate is difficult to separate the chip by cleavage, and it is not easy to obtain the resonator end face required for the laser diode (LD) by cleavage. For this reason, at present, resonator end faces are formed by dry etching, or after forming a sapphire substrate to a thickness of 100 μm or less, resonator end faces are formed in a form close to cleavage. In this case as well, it is impossible to easily separate the resonator end face and the chip as in the conventional LD in a single process, resulting in process complexity and cost.

In order to solve these problems, it is eager to use GaN substrates. Thick films are formed on GaAs and sapphire substrates using HVPE (hydride vapor phase epitaxy), and these substrates are removed later. Japanese Patent Laid-Open No. 2000-12900 and Patent Document 2 (Japanese Patent Laid-Open No. 2003-178984) propose a method for performing the above.
In addition, the sapphire substrate has low thermal conductivity (42 W / m · K), so it is not suitable for high-power optical devices and electronic devices. The thermal conductivity of GaN crystals is 130 W / m · K, and the GaN substrate is superior to the sapphire substrate in this respect.

However, in order to achieve higher output, a substrate material with higher thermal conductivity is desired.
Non-Patent Document 1 (Japanese Journal of Applied Physics, Vol. 41 (2002) Pt. 2, No. 12B, pp. L1434-1436) realizes higher heat conduction by the following measures. .

1. First, an AlGaN LED structure is formed on a sapphire substrate via a GaN layer, and an Au electrode is formed on the surface.
2. Thereafter, CuW is attached to the LED structure via an Au-based electrode.
3. Thereafter, the sapphire substrate is peeled off by a laser lift-off method using a KrF laser.
4). Further, the GaN layer is removed by polishing.
5. A Ti—Al electrode is formed on one side of the AlGaN-based LED from which the GaN has been removed.

As a result, by turning upside down, a light emitting diode of a CuW substrate is realized (third prior art).
Currently, InGaAlN-based (Group III nitride) devices used as purple-blue-green light sources are mainly used for MO-CVD (metal organic chemical vapor deposition) and MBE ( It is manufactured by crystal growth using molecular beam crystal growth method.

  As a problem when sapphire or SiC is used as a substrate, there is an increase in crystal defects caused by a large difference in thermal expansion coefficient and lattice constant from the group III nitride. For this reason, it leads to the fault that device characteristics are bad, for example, it is difficult to extend the lifetime of the light emitting device, or the operating power is increased.

  Furthermore, in the case of a sapphire substrate, since it is insulative, it is impossible to take out the electrode from the substrate side as in the conventional light emitting device, and it is necessary to take out the electrode from the nitride semiconductor surface side where the crystal has grown. . As a result, there is a problem that the device area becomes large, leading to high costs. Further, the group III nitride semiconductor device fabricated on the sapphire substrate is difficult to separate the chip by cleavage, and it is not easy to obtain the resonator end face required for the laser diode (LD) by cleavage. For this reason, at present, resonator end faces are formed by dry etching, or after forming a sapphire substrate to a thickness of 100 μm or less, resonator end faces are formed in a form close to cleavage. In this case as well, it is impossible to easily separate the resonator end face and the chip as in the conventional LD in a single process, resulting in process complexity and cost.

CuW has a higher thermal conductivity of 190 W / m · K compared to sapphire and GaN substrates, making it suitable for higher-power semiconductor devices. However, in the case of the third prior art, 1 to 5 complicated processes are required, leading to an increase in cost.
On the other hand, the present inventors have been eager to realize a high-quality group III nitride crystal by reacting a mixed melt composed of an alkali metal and a group III metal with a group V raw material containing nitrogen. (For example, JP 2001-058900, JP 2001-064097, JP 2001-64098, JP 2001-102316, JP 2001-119103, JP 2002-128586, JP 2002-128587, JP 2002-201100, JP 2002-326898, JP 2002-338391, JP 2003-012400, JP 2003-081696, JP 2003-160399, JP 2003-238296, JP 2003 206198, JP2003-212696, US Pat. No. 65 Is a method called a flux method disclosed in 2633 Pat.).
Japanese Patent Laid-Open No. 2000-12900 JP 2003-178984 A Japanese Journal of Applied Physics, Vol. 41 (2002) Pt. 2, No. 12B, pp. L1434-1436

The object of the present invention is to further develop the flux method that has been invented so far, and to improve the heat dissipation with higher quality than the first conventional technology and the second conventional technology (to increase the thermal conductivity). The purpose is that. Furthermore, it is to realize a low-cost and high thermal conductivity group III nitride crystal manufacturing method that does not lead to an increase in cost, which is a problem in the third prior art.

Specifically, an object of claim 1 is to realize a group III nitride crystal of low cost, high quality and high thermal conductivity .

The present invention has been made to achieve the above-described object. Specifically, in claim 1, in the reaction vessel, a mixed melt containing at least a group III metal and a flux and at least nitrogen are contained in the reaction vessel. In the Group III nitride crystal manufacturing method, wherein a Group III nitride crystal is grown by reacting a Group III metal and nitrogen from a substance containing a substrate, the substrate is made of the Group III nitride surface material. A step of installing in a mixed melt, a step of supplying a substance containing at least nitrogen into the reaction vessel and forming a recess due to a crystal defect in the substrate under a condition that a group III nitride does not grow crystal; The step includes filling the recess with a melt of at least one of a group III metal or a flux and growing a group III nitride crystal over the recess.

In claim 1, a group III nitride constituted by reacting a group III metal and nitrogen from a flux, a mixed melt containing at least a group III metal, and a substance containing at least nitrogen is grown in a reaction vessel. In the Group III nitride crystal manufacturing method, a step of placing a substrate whose surface material is made of Group III nitride in the mixed melt, supplying the substance containing at least nitrogen into the reaction vessel, and III Forming a recess due to crystal defects on the substrate under a condition in which the group nitride does not grow , filling the recess with at least one melt of a group III metal or flux, and covering the recess with III A group III nitride crystal manufacturing method characterized by including a step of growing a group nitride crystal, thereby realizing a high quality and high thermal conductivity group III nitride crystal growth method at a low cost. Rukoto can be.
In other words, when a crystal is grown by the flux method, a group III nitride crystal is filled with a high thermal conductivity group III metal or flux or a mixed melt of group III metal and flux. It is possible to realize a group III nitride crystal in which a crystal defect in the product crystal terminates in this recess and the crystal defect has a high thermal conductivity. As a result, a complicated process as described in the third prior art is not necessary, leading to cost reduction.

According to the first aspect of the present invention, in the reaction vessel, the flux and the substance containing at least a group III metal form a mixed melt, and from the mixed melt and the substance containing at least nitrogen, the group III metal and nitrogen are used. In a group III nitride crystal growth method (hereinafter referred to as a flux method) for growing a group III nitride crystal, a group III metal or a flux or a group III metal and a flux It is a group III nitride crystal growth method characterized by filling a mixed melt.
The flux referred to in the present invention refers to a substance that can be formed at a lower temperature and a lower pressure than a normal reaction temperature and pressure in which a group III nitride is formed only from a group III metal and nitrogen. That is, as the flux, in addition to the group III nitride, an alkali metal such as Li, Na, K, an alkaline earth metal, or a mixture thereof can be used.

  Examples of the substance containing nitrogen include nitrogen gas, azide compounds (for example, sodium azide, potassium azide and other azide compounds and any mixture thereof), and compounds containing nitrogen as a constituent element such as ammonia. B, Ga, Al, In, etc. are applicable as the group III metal (group III compound). Here, boron (B) is not a metal, but as a group III material constituting BN as a group III nitride, in the present invention, the expression group III metal means that a group III compound other than a metal is a group III metal. There is.

Further, the mixed melt used in the present invention may be prepared as a substance containing a flux and at least a group III metal from the beginning, or may form a substance containing a flux and at least a group III metal in the process of crystal growth. Either is fine.
The interface mentioned here is a boundary region between a substrate for growing a group III nitride crystal by the flux method and a crystal grown by the flux method, and an intermediate region when the group III nitride crystal is grown by the flux method. Either can be applied. That is, when a crystal is grown by the flux method, a group III metal crystal or a flux or a mixed melt of a group III metal and a flux is filled in a group III nitride crystal.

  The present invention will be further described in detail with reference to the following examples. However, these examples are only part of the present invention, and the present invention is a technical idea including these examples.

[Example 1]
A first embodiment will be described with reference to FIGS. The first embodiment relates to claim 1 . FIG. 1 is a cross-sectional view of a group III nitride crystal growth apparatus using a flux method. FIG. 2 shows a substrate having an uneven shape. 3 is a cross-sectional view of a group III nitride crystal grown on the substrate of FIG. 2 using the apparatus of FIG.

There is a second reaction vessel 113 inside the first reaction vessel 101, and a temperature at which the group III nitride can grow crystals between them (inside the first reaction vessel 101 and outside the second reaction vessel 113). A heating device 106 is provided so that it can be controlled. Inside the second reaction vessel 113, a mixed melt holding vessel 102 is installed. In the mixed melt holding container 102, there is a mixed melt 103 composed of Ga as a substance containing at least a group III metal and Na as an alkali metal. There is a lid 109 on the mixed melt holding container 102. There is a slight gap between the mixed melt holding container 102 and the lid 109 so that gas can enter and exit.
A thermocouple 112 for detecting the temperature of the mixed melt holding container 102 is installed in the second reaction container 113. The thermocouple 112 is connected to the heating device 106 so that temperature feedback control is possible.

  For example, nitrogen gas is used as the substance containing at least nitrogen. Nitrogen gas can be supplied from the nitrogen gas container 107 installed outside the first reaction container 101 to the space 108 in the first reaction container and the second reaction container through the gas supply pipe 104. I can do it. In order to adjust the pressure of the nitrogen gas, a pressure adjusting valve 105 is provided. A pressure sensor 111 for detecting the pressure of nitrogen gas in the reaction vessel is installed. At this time, the pressure sensor 111 is fed back to the pressure adjustment valve 105 so that the respective pressures in the first reaction vessel and the second reaction vessel are substantially the same pressure and become a predetermined pressure. It has become.

On the other hand, the substrate shown in FIG. 2 is a GaN (gallium nitride) substrate 110 which is one of group III nitrides. The GaN substrate 110 has a concave portion 201 and a convex portion 202. Further, the crystal defect 203 described in the prior art is present in the GaN substrate and penetrates to the crystal surface. The GaN substrate 110 may be grown by a flux method or may be grown by another method such as VPE or MO-CVD.
A GaN crystal is grown on the GaN substrate 110 of FIG. 2 using the group III nitride crystal growth apparatus by the flux method of FIG. The nitrogen pressure in the reaction vessel of FIG. 1 is set to 4 MPa, the temperature of the mixed melt holding vessel 102 is set to 775 ° C., and the ratio of Na to Ga in the mixed melt 103 is set to 4: 6. A GaN crystal is grown on the GaN substrate 110 (first GaN crystal) by placing the GaN substrate 110 in the mixed melt and maintaining the temperature and pressure in this state.

The GaN crystal newly grown by this flux method is the second GaN crystal 301 in FIG. That is, the second GaN crystal 301 is grown on the GaN substrate 110.
The second GaN crystal 301 grown at this time grows faster in the substrate surface direction (lateral direction in the figure) than in the vertical direction (upward direction in the figure) of the GaN substrate 110. As a result, it is possible to grow the second GaN crystal 301 while leaving the substrate recess 201. Here, the GaN substrate surface is the C plane, that is, the (0001) plane, and the direction perpendicular to the substrate surface is the <0001> direction.

At this time, the recess 201 originally in the substrate is filled with a mixed melt of Ga, which is a Group III metal material, and Na, which is a flux.
Further, the crystal defect 203 penetrates to the surface of the newly grown GaN crystal in the substrate convex portion 202, but terminates at the interface with the filled mixed melt in the substrate concave portion 201. Therefore, the crystal defect density is reduced on the GaN crystal surface newly grown by the flux method.
Further, since the mixed melt is filled, the thermal conductivity in this region is increased, and the heat dissipation characteristics are improved.

  By growing a GaN crystal on the concavo-convex substrate by the flux method, a high-quality GaN crystal having a low defect density and a high thermal conductivity can be obtained without going through the complicated steps described in the prior art. It can be produced. That is, both low cost and high quality can be achieved.

[Example 2]
A second embodiment will be described with reference to FIGS. The second embodiment relates to claim 1 .
FIG. 4 shows a cross section of the GaN substrate 401. The GaN substrate 401 is grown by using a MOVPE method, a HVPE method, or the like, but its manufacturing method is not particularly specified. The GaN substrate 401 has crystal defects 402 penetrating to the crystal surface.
A recess 501 is formed on the surface of the GaN substrate 401 using the apparatus of the flux method shown in FIG. FIG. 5 shows a cross section thereof. Since the description of FIG. 1 is described in the first embodiment, it is omitted here.
First, the GaN substrate 401 shown in FIG. 4 is placed in the mixed melt shown in FIG. Although the GaN crystal 110 is illustrated in FIG. 1, the GaN substrate 401 of FIG.
Using the apparatus of FIG. 1, the temperature of the mixed melt holding container 102 and the nitrogen pressure are set to 900 ° C. and 2 MPa, respectively. By holding the GaN substrate 401 in this state, the recess 501 of the GaN crystal shown in FIG. 5 can be formed. The concave portion 501 of the GaN crystal is generated due to the crystal defect 402.

Next, the temperature of the mixed melt holding container 102 and the nitrogen pressure are set to 775 ° C. and 6 MPa, respectively. By holding the GaN crystal having the recesses in FIG. 5 in this state, the GaN crystal grows thereon. FIG. 6 shows a cross section of the GaN crystal. On the GaN substrate 401 having the recess 501 of FIG. 5, there is a newly grown second GaN crystal 601.
The second GaN crystal 601 grown at this time grows faster in the surface direction of the substrate (horizontal direction in the figure) than in the vertical direction of the GaN substrate 110 (upward direction in the figure). As a result, it is possible to grow the second GaN crystal 601 while leaving the substrate recess 501. Here, the GaN substrate surface is the C plane, that is, the (0001) plane, and the direction perpendicular to the substrate surface is the <0001> direction.
At this time, the concave portion 501 originally in the substrate is filled with a mixed melt 602 of Ga which is a group III metal raw material and Na which is a flux.
Further, the crystal defect 402 terminates at the interface with the mixed melt 602 filled in the substrate recess 501. Therefore, the crystal defect density is reduced on the GaN crystal surface newly grown by the flux method.
Further, since the mixed melt is filled, the thermal conductivity in this region is increased, and the heat dissipation characteristics are improved.

By growing a GaN crystal on the concavo-convex substrate by the flux method, a high-quality GaN crystal having a low defect density and a high thermal conductivity can be obtained without going through the complicated steps described in the prior art. It can be produced. That is, both low cost and high quality can be achieved.
In addition, it is possible to form concavo-convex shapes on GaN crystals by using the flux method equipment and method, and it is possible to realize concavo-convex shape formation, GaN crystal growth, and mixed melt filling with the same equipment at low cost. , Leading to higher quality.

[Example 3]
A third embodiment of the present invention will be described with reference to FIG. This third embodiment relates to claim 1 .
Crystal growth is performed using the group III nitride crystal growth apparatus according to the flux method of FIG. 1 described in the first and second embodiments. Since the description of FIG. 1 is described in the first embodiment, it is omitted here.
FIG. 7 is a cross section of a GaN crystal grown according to this example.
First, the first GaN crystal 701 is grown using the apparatus of the flux method of FIG. The growth conditions of the first GaN crystal 701 are that the temperature of the mixed melt holding container 102 and the nitrogen pressure in FIG. 1 are 775 ° C. and 4 MPa, respectively. Next, the temperature of the mixed melt holding container 102 is kept at 775 ° C., and the nitrogen pressure is increased to 8 MPa. By doing so, the second GaN crystal 702 grows. At this time, as the nitrogen pressure increases, the growth rate is faster in the surface direction of the substrate (lateral direction in the figure) than in the vertical direction (upward direction in the figure) of the GaN substrate 110. As a result, the third GaN crystal 704 grows on the second GaN crystal 702 while the recess 703 is formed as a region where a part of the GaN crystal does not grow in the lateral direction. Here, the GaN substrate surface is the C plane, that is, the (0001) plane, and the direction perpendicular to the substrate surface is the <0001> direction.

Here, the concave portion 703 is filled with a mixed melt 602 of Ga which is a group III metal raw material and Na which is a flux. Since this mixed melt is filled, the thermal conductivity in this region is increased, and the heat dissipation characteristics are improved.
Further, the GaN crystal grown by the flux method has fewer crystal defects than the GaN crystal formed by the other methods described in the first and second embodiments. As a result, a high-quality GaN crystal having a low defect density and a high thermal conductivity can be produced without going through the complicated steps described in the prior art. That is, both low cost and high quality can be achieved.
In addition, it is possible to form concavo-convex shapes on GaN crystals by using the flux method equipment and method, and it is possible to realize concavo-convex shape formation, GaN crystal growth, and mixed melt filling with the same equipment at low cost. , Leading to higher quality.

[Example 4]
A fourth embodiment of the present invention will be described with reference to FIG . FIG. 8 is a perspective view of a semiconductor laser which is an application example of the group III nitride semiconductor device of the present invention.
The GaN-based thin films 802 to 707 are grown on the GaN substrate 801 described in the first to third embodiments, in which the density of crystal defects is low and the mixed melt is filled in the recesses. At this time, the inside of the GaN substrate 801 is filled with the mixed melt 811 described in the first, second and third embodiments.
On the GaN substrate 801, an n-type AlGaN layer 802, an n-type GaN layer 803, an InGaN MQW (multiple quantum well) layer 804, a p-type GaN layer 805, a p-type AlGaN layer 806, and a p-type GaN layer 807 are sequentially crystallized. Has grown. As this crystal growth method, a thin film crystal growth method such as MO-VPE (metal organic chemical vapor deposition) method or MBE (molecular beam epitaxy) method is used.

Since these GaN-based thin films 802 to 807 are suitable for thin film growth such as MOVPE and MBE, p-type and n-type conductivity control, carrier concentration control, and mixed crystal composition control of GaN, AlN, InN It is possible to grow a thin film for a device.
As described above, since the crystal defect terminates in the vicinity of the interface with the mixed melt of the concave portion of the GaN crystal, it is very small in the region of the device thin film 802 to 807.
A ridge structure is formed in the laminated film of GaN, AlGaN, and InGaN, and an SiO ₂ insulating film 808 is formed in a state where only the contact region is opened. Electrode Al / Ti 810 is formed.

By injecting current from the p-side ohmic electrode Au / Ni 809 and the n-side ohmic electrode Al / Ti 810 of this semiconductor laser, laser oscillation occurs and laser light is emitted in the direction of the arrow in the figure.
Since this semiconductor laser uses the GaN crystal of the present invention as a substrate, there are few crystal defects in the semiconductor laser device, and since the mixed melt 811 is inside the substrate, the heat dissipation characteristics are good. As a result, a device with a high output operation and a long life can be realized.
In addition, since the GaN substrate is n-type, electrodes can be formed directly on the substrate. When an insulating substrate such as a conventional sapphire substrate is used, two electrodes on the p-side and n-side are formed only from the surface. There is no need to take out, and the cost can be reduced. Furthermore, the light emitting end face can be formed by cleavage, and in combination with chip separation, a low-cost and high-quality device can be realized.

In this embodiment, InGaN MQW is used as the active layer, but the emission wavelength can be shortened using AlGaN MQW as the active layer. Since there are few defects and impurities in the GaN substrate, light emission from a deep order is reduced, and a highly efficient light-emitting device is possible even when the wavelength is shortened.
In this embodiment, application to an optical device has been described. However, application to an electronic device is also applicable to the present invention. In other words, by using a GaN substrate with few defects and excellent heat dissipation characteristics, the GaN-based thin film epitaxially grown on the GaN substrate has few crystal defects, and as a result, leakage current can be suppressed, and the carrier confinement effect in the case of a quantum structure can be achieved. A high performance device with high output and high output can be realized.

[Example 5]
A fifth embodiment of the present invention will be described with reference to FIG. FIG. 9 is a perspective view of the group III nitride semiconductor module of the present invention.
On the submount 901, III-nitride semiconductor device 903 is mounted. The group III nitride semiconductor device 903 is filled with the mixed melt in the surface direction of the submount 901 shown in FIG.
A heat sink 902 is installed in a direction substantially orthogonal to the submount 901. The heat sink 902 and the group III nitride semiconductor device 903 are mounted at positions where they contact each other.
In this state, when the group III nitride semiconductor device 903 operates, heat is generated, but heat is conducted to the heat sink through the mixed melt inside the group III nitride crystal. At this time, since the thermal conductivity of the mixed melt is high, efficient heat dissipation is possible. As a result, a large output operation of the semiconductor device becomes possible.
The group III nitride semiconductor device described in this embodiment can be applied to any optical device such as a light emitting diode or semiconductor laser, or an electronic device such as a field effect transistor, as long as it is a semiconductor device for high output.

1 is a diagram showing a flux growth crystal apparatus according to Example 1. FIG. 1 is a cross-sectional view of a group III nitride crystal according to Example 1. FIG. 1 is a cross-sectional view of a group III nitride crystal according to Example 1. FIG. 3 is a cross-sectional view of a group III nitride crystal according to Example 2. FIG. 3 is a cross-sectional view of a group III nitride crystal according to Example 2. FIG. 3 is a cross-sectional view of a group III nitride crystal according to Example 2. FIG. 6 is a cross-sectional view of a group III nitride crystal according to Example 3. FIG. 6 is a perspective view of a group III nitride semiconductor device according to Example 4. FIG. 7 is a perspective view of a group III nitride semiconductor module according to Example 5. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 1st reaction container 102 Mixed melt holding container 103 Mixed melt 104 Gas supply pipe 105 Nitrogen pressure regulating valve 106 Heating device 107 Nitrogen gas container 108 Space in reaction container 109 Lid of mixed melt holding container 110 GaN crystal 111 Pressure sensor 112 Thermocouple 113 Second reaction vessel 201 Concave portion of GaN substrate 202 Convex portion of GaN substrate 203 Crystal defect (dislocation)
301 Second GaN crystal 401 GaN substrate 402 Crystal defect (dislocation)
501 Concave part of GaN crystal 601 Second GaN crystal 602 Mixed melt 701 First GaN crystal 702 Second GaN crystal 703 Concave part 704 Third GaN crystal 801 n-type GaN substrate 802 n-type AlGaN clad layer 803 n-type GaN Guide layer 804 InGaN MQW active layer 805 p-type GaN guide layer 806 p-type AlGaN cladding layer 807 p-type GaN contact layer 808 SiO ₂ insulating film 809 p-side ohmic electrode 810 n-side ohmic electrode 811 mixed melt 901 submount 902 heat sink 903 Group III nitride semiconductor devices

Claims (1)

A group III nitride crystal for growing a group III nitride formed by reacting a group III metal and nitrogen from a flux, a mixed melt containing at least a group III metal, and a substance containing at least nitrogen in a reaction vessel In the manufacturing method,
Installing a substrate having a surface material made of group III nitride in the mixed melt;
Supplying the substance containing at least nitrogen into the reaction vessel and forming a recess due to crystal defects on the substrate under the condition that the group III nitride does not grow crystal; and
Filling the recess with a melt of at least one of group III metal or flux;
And a step of growing a group III nitride crystal so as to cover the recess.

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